Method for controlling the firing angle of an electric motor

ABSTRACT

Disclosed is a method for controlling the firing angle of a signle-phase AC powered electric motor which is triggered by means of at least one locking electronic switch, especially a triac (T 1  and T 4 ) located between the distribution voltage (U V ) and at least one motor winding (A, B). According to said method, intervals are defined within which the triacs (T 2  to T 4 ) are to be fired according to the curve of the distribution voltage (U V ) and the voltage (U EMK ) induced in the respective winding in order to allow the motor to start as quickly and smoothly as possible and run quietly and at high efficiency.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/EP2004/000281, filed Jan. 16, 2004, which was published in theGerman language on Aug. 5, 2004, under International Publication No. WO2004/066484 A1 and the disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

The invention relates to a method for controlling the firing angle of asingle-phase electric motor supplied with alternating current.

Electric motors nowadays may be activated largely independently of themains frequency by way of electronic controls. However, even with theapplication of highly integrated electronic circuits, converterelectronics create costs which often lie in the magnitude of that of themotor. For this reason, and in particular for motors of a small andmedium power of below 200 Watts for example, one strives to providecontrols which may be manufactured in a more economical manner and whichoperate the motor in a highly effective manner, i.e. at a highefficiency. In particular, permanent magnet motors which are providedwith activation electronics constructed from triacs as power switchesare suitable for this on account of their high efficiency. Such triacswhich are allocated as switches to the individual motor windings havethe advantage that they may be manufactured in an inexpensive manner,but have the disadvantage that with the usual activation it is the caseof locking switches, i.e. which after switching on only block again whenthe current flowing through the switch becomes zero or changes itsdirection.

A method for the activation of a brushless electric motor by way oftriacs is known from DE 35 07 883 A1 with which the mains voltage isconnected to the part windings of the stator winding by way ofphase-angle control such that one may also activate rotational speedsbelow the synchronous speed, but only certain rotational speeds whichmay not be freely selected.

A method for controlling a brushless electric motor is known from DE 3517 570 A1, which likewise by way of triacs temporarily applies the mainsvoltage to the oppositely directed part windings of the motor winding,so that the motor may be activated at rotational speeds which lie abovethe synchronous speed by way of the production of opposing magnet poles.By way of this, the rotational speed may assume a multiple value of thesynchronous speed, but only integer multiples of the synchronous speed.

It is thus known to activate an AC-supplied electric motor by way oftriacs such that this may not only be operated synchronously, butsupersynchronously and subsynchronously. As such, a further field ofapplication opens up also to single-phase electric motors supplied withalternating current, which until now were only able to be controlled inrotational speed by way of extensive converter electronics.

However, phase-angle control as such is not sufficient in order toachieve a reliable start, a smooth running and a high efficiency onoperation, and finally in order to avoid the magnets of the rotorbecoming damaged due to an unallowably high magnetic field of thestator. This problem is described in DE 195 34 423 A1. For solving thisproblem, it is suggested there to provide a sensor for measuring themagnetic field of the rotor and with the help of phase-angle control toswitch the alternating voltage to the stator winding of the motordepending on the magnetic field sensor signal, such that a moment isproduced in the rotational direction. At the same time the current islimited in order not to produce any undesired high magnetic fields inthe stator.

The disadvantage with this method is the fact that at least one magneticfield sensor is required for detecting the rotor position. Furthermore,the current limitation is achieved by way of measuring and integratingthe currents and voltages and adapting them according to the rotor orthe positions of the magnets.

BRIEF SUMMARY OF THE INVENTION

Against this background, it is the object of the invention to create amethod for controlling the firing angle of a single-phase electric motorsupplied with an alternating current, by way of at least one lockingelectronic switch between the mains supply and at least one motorwinding, which with regard to control technology may be carried out withsimple means and results in a reliable and quick start, as well as asmooth running at a constant, freely selectable rotational speed at ahigh efficiency. Furthermore, the method where possible is to be able tobe realised without mechanical sensors on the motor.

According to the invention, the features specified in claim 1 achievethis object. Advantageous designs of the invention are specified in thedependent claims, the subsequent description as well as the drawing.

The basic concept of the present invention are the firing rules whichare specified in claim 1 according to a) to f), which are appliedselectively or preferably in combination and thus ensure a secure andoptimised start and also permit the activation of the motor at almostany rotational speed in a simple manner, at a high efficiency and with asmooth running. The firing rules may be implemented by way of angularconsiderations or time measurements between the zero-crossings of thesupply voltage and a variable corresponding to the rotor position andthe rotor speed.

The method according to the invention presupposes in particular lockingelectronic switches, thus triacs for example, which are comparativelyinexpensive, and at the same time in particular also takes account ofthe problems with regard to circuit technology (locking) which arisewith regard to this context.

The sensor technology which is required for implementing the method maybe purely electronic and thus may form a part of the control/regulation.

In order to ensure that the winding to be connected is not subjected toa voltage which produces a moment which opposes an intended rotationaldirection of the rotor, the voltage induced in the winding to beconnected, thus the EMF (electromotive force) is to be evaluated and itis to be ensured that a connection of this winding is only effected whenthe supply voltage has the same polarity as the EMF (rule a).

At the same time a connection of this winding is preferably onlyeffected when the voltage (EMF) induced in the winding to be connectednot only has the same polarity as the supply voltage, but is also issmaller that this with regard to its magnitude (rule b).

The further essential firing rule lies in the fact that the winding tobe connected is only subjected to the supply voltage within anpredefined angular range calculated beginning from the zero-crossing ofthe induced voltage (EMF) in this winding, and specifically only whenthe induced voltage and the supply voltage have the same polarity (rulec).

A further essential firing rule finally lies in the fact that theconnection of a winding is only effected when the zero-crossing of thesupply voltage leads the zero-crossing of the voltage (EMF) induced inthe winding to be connected, this latter zero-crossing being expectednext based on the history of the course of the signal of the EMF, giventhe same change in polarity. This means that a connection of the windingis only effected when the zero-crossing of the EMF signal from plus tominus lags the zero-crossing of the supply voltage from plus to minus orfrom minus to plus when the zero-crossings which are offset in each caseby 180° are considered. Since this firing rule may only be determined inan exact manner when the point in time of firing which is givenaccording to this firing rule has already past, for a practicalapplication one must determine the respective zero-crossing which is tobe expected next from the history of the EMF signal, in order to be ableto apply the rule in a practical manner at all. It is evident that theaccuracy with which the expected zero-crossing of the EMF signal may beevaluated becomes higher, the more the rotational speed approximates aconstant rotational speed. This firing rule is thus in particularadvantageously applicable for the activation at a constant rotationalspeed (rule d).

The previously mentioned firing rule may be specified further in that afiring, i.e. connection of the triac for the conductive connection ofthe supply voltage to the winding to be connected is only effected whenthe angle between the voltage (EMF) induced in the winding to beconnected and the supply voltage assumes a predefined value. This firingrule is also particularly advantageous for the activation at a constantrotational speed (rule e), where no acceleration excess is required,thus the firing range resulting according to the rule d does not need tobe fully exploited.

Alternatively the switching point in time is preferably selected suchthat the angle between the point in time when the current in the windingto be connected assumes zero up to the point in time in which theinduced voltage in this winding has assumed the value zero correspondsto the angle or the factor of this angle which preferably is betweenbetween 0.5 and 2, which lies between the previous zero-crossing of theinduced voltage and the current point in time of firing. This firingrule too is particularly advantageous for the activation at a constantrotational speed, and with regard to the signal course of the supplyvoltage effects a largely symmetrical connection of the respectivewinding (rule f). Rule f however in comparison to rule e demands a highcomputing capability.

On taking into account one or preferably more of the previouslymentioned conditions, the motor is started in a rapid manner and isoperated at any rotational speed with a good efficiency, and may beactivated at any rotational speed by way of a [closed-loop] controlcircuit. Furthermore, the firing method according to the inventionensures a particularly smooth running of the motor which is particularlyadvantageous with the application in the field of heating circulationpumps, whose noise emissions are transmitted further through the pipenetwork in an almost undamped manner.

It is particularly advantageous if the angle according to firing rule eis selected depending on the rotational speed and separately for eachphase, since the angle of the geometric offset to the other phases needsto be adapted.

Preferably, the firing rules c and d, according to which the connectionof the winding is only effected when the voltage induced in the windingto be connected lies in a predefined angular range with respect to itszero-crossing, assuming the same polarity of the induced voltage and thesupply voltage, as well as when the zero-crossing of the supply voltagelies in front of the expected zero-crossing of the voltage induced inthe winding to be connected, assuming the same signal direction, areapplied for the subsynchronous run-up (starting of the motor oracceleration in the subsynchronous range). For the supersynchronousrun-up, i.e. the acceleration of the motor in the supersynchonous rangeto a desired supersynchronous rotational speed, it is however preferableto apply the firing rule d, since a temporary braking moment isprevented with this rule. Firing rule e is to be advantageously selectedfor the operation of the motor at a constant rotational speed, sincethen a particularly smooth and uniform running of the motor is ensuredwith a maximal efficiency.

Preferably with the method according to the invention, the voltageinduced in a winding, in particular its zero-crossing is detected, andspecifically when the supply voltage is disconnected. These values mayalternatively be evaluated by calculation taking the rotor position intoaccount.

With the method according to the invention, the detection of thereadings, in particular the EMF in the winding separated from the mainsmay be effected with technically comparatively simple means in that oneevaluates whether the winding is in the condition without current, andsubsequently the EMF is determined by way of connecting a measurementmeans for measuring the voltage difference across the winding. Theevaluation of the condition without current may be effected as isdescribed below. One the one hand the zero-crossings are to be detected,which is not a problem with regard to measurement technology since onedoes not need to evaluate a specific value but only the change inpolarity. According to a further formation of the invention it mayhowever also be necessary for controlling the firing angle to detect thevoltage induced in the winding to be connected in order to ascertainwhether this with regard to magnitude is smaller than the supply voltageor not. This may be effected in a simple manner in that the voltageacross the switch which connects or disconnects the winding to and fromthe mains supply and whose EMF is to be evaluated is measured. Since themains voltage constantly prevails on the one side of this switch and onthe other side the induced voltage (EMF) of the winding, with ameasurement across the switch, the difference of the voltages alwaysresults, so that for the method according to the invention one onlyneeds to effect an evaluation of this measurement with regard topolarity. This means that the voltages with regard to their magnitudedoe not need to be detected at all, but only the polarity of thedifferential voltage resulting here, which is simple to evaluate withregard to measurement technology. The change in polarity heresimultaneously represents the point in time when the winding currentassumes the value zero.

Advantageously, according to the method according to the invention, notonly are the zero-crossings of the induced voltages (EMF) in thewindings, but also the zero-crossings of the supply voltage aredetermined and evaluated with regard to the point in time of firing.This embodiment which determines and evaluates the zero-crossings of thesupply voltage and of the EMF, and the voltage across the switch inorder to realise the firing rules, is based purely on time measurementsand angular considerations without having to detect quantitativeelectrical variables. This construction is therefore particularly simpleand robust.

On account of the relationships of the windings to one another which aregeometrically fixed, the predefined angular range of the voltage (EMF)induced in the winding to be connected may be determined by determiningthe zero-crossing of the voltage induced in the other pole, andspecifically when taking the geometric pole arrangement into account.Therefore one does not need to constantly observe the EMF of the windingwhich is just to be switched, but any other winding may be used forevaluation whilst taking account of its angular position, inasmuch as itconcerns the evaluation of the zero-crossings.

Instead of a signal detection of the EMF via a measurement in a windingseparated from the mains supply, one may also provide for detection bysensor. In particular the zero-crossings of the EMF may be determined bya sensor detecting the rotor position and in a calculated manner. A Hallsensor or another electronic sensor may serve as a sensor. At the sametime advantageously a separate sensor is allocated to each phase of themotor in a manner such that the polarity change of the magnetic fielddetected by the sensor corresponds to the zero-crossing of the voltage(EMF) induced in the winding to be connected. Specifically, with asuitable allocation one may use the sensor signal, at least inasmuch asit concerns the zero-crossing, since as far as this is concerned itcorresponds to the EMF. One therefore requires no signal processingwhich takes account of the angle.

In order to be able to detect the EMF of a winding in the connectedcondition, one may detect the EMF in another winding which is notconnected at this point in time, thus is not connected to the mainssupply, wherein then a corresponding calculated phase-shifting iseffected according to the geometric allocation of these two windings, sothat an EMF signal results which represents the EMF in the connectedwinding.

The predefined angular range of the EMF in which the firing, i.e. theconnection of the winding to the mains supply is to be effected, dependson the design of the motor. With a four-pole (four-phase) motor, thefiring is effected preferably in the first 90° degrees of the EMF,assuming the same polarity of the induced voltage and the supplyvoltage.

In order to observe the predefined angular range in which the firing isto be effected according to rule c or d as precisely as possible, it isuseful to carry out a corresponding time measurement in preferably thelast half period of the voltage induced in the winding to be connected,in order to be able to predict the next expected zero-crossing of theEMF in an as reliable as possible manner and from this to determine thepreferred firing angle range.

A corresponding single-phase electric motor supplied with alternatingcurrent with a permanent magnet motor comprises at least one windingwhich is arranged in the stator and which is subjected to the supplyvoltage by way of a locking electronic switch, in particular a triac.With such an arrangement, preferably at least one further lockingelectronic switch is provided to which a phase-shifting component may beconnected. A triac is preferably likewise used as an electronic switch,wherein the phase-shifting component is preferably a capacitor. By wayof this one may achieve a particularly smooth running of the motor ifthe capacitor is connected after the starting.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofthe invention, will be better understood when read in conjunction withthe appended drawings. For the purpose of illustrating the invention,there are shown in the drawings embodiments which are presentlypreferred. It should be understood, however, that the invention is notlimited to the precise arrangements and instrumentalities shown.

In the drawings:

FIGS. 1–5 shows in each case different signal courses by way of withwhich the firing rules are to be explained by way of example; and

FIG. 6 shows a circuit diagram of a single-phase, two-pole electricmotor supplied with alternating current.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 in total shows five diagrams a, b, c, d and e, whose time axesrun horizontally and correspond to one another. The temporal course ofthe supply voltage U_(V) as well as the temporal course of the voltageU_(EMF) induced in a winding are plotted in FIG. 1 a. Whilst the supplyvoltage U_(V) represents the common 50 Hz alternating voltage signal,the course of the induced voltage U_(EMF) displays a typical startingbehaviour. At the beginning of the rotation of the rotor, the voltageinduced in the winding increases only gradually, and with this, theperiod corresponds to the reciprocal rotor speed. According to thefiring rule a, the supply voltage U_(V) is only to be connected to thewinding when the voltage U_(EMF) induced in this winding has the samepolarity as the supply voltage U_(V). The polarity of the supply voltageU_(V) over its temporal course is represented in FIG. 1 d, wherein thevalue zero corresponds to a negative polarity and the value 1 to apositive polarity. For the application of the first condition,specifically that the voltage U_(EMF) induced in the winding to beconnected has the same polarity as the supply voltage U_(V), one onlyneeds to determine when the curves according to FIGS. 1 b and 1 c matchwith regard to their values (0 or 1). This condition is then fulfilled.

As is to be deduced from FIG. 1 d, here however firing rule b is alsoverified, specifically that the voltage U_(EMF) induced in the windingto be connected and having the same polarity is smaller than supplyvoltage with regard to magnitude. For this, it is plotted in FIG. 1 dwhen the latter is the case, specifically in the regions of the curve inwhich the curve assumes the value 1.

The switching times which result according to rule a and b are thenshown by way of FIG. 1 e. FIG. 1 e represents when the signal of thecurves 1 b, 1 c and 1 d is simultaneously 1 or when one or more of thesecurves does not assume the value 1. FIG. 1 e thus in the regions of thecurve in which the value 1 is indicated, indicates the time intervalsfor connecting the winding which are possible according to theapplication of the rules a and b, i.e. for switching the triac forconnecting the winding to the supply voltage supply. The time intervalsin which the curves according to FIG. 1 e has the value 1 of course onlyrepresent the possible switching times of the respective triac, thedisconnection is effected automatically on account of the locking, andspecifically when the winding current assumes the value zero. Thedisconnection times are thus neither indicated in this nor in thefollowing diagrams, only the possible switching times.

The switching times which result according to firing rule c areexplained by way of FIG. 2. Firing rule c states that the voltageU_(EMF) induced in the winding to be connected is located in apredefined angular range with respect to its zero-crossing, wherein thesame polarity of the induced voltage and the supply voltage is assumed.This angular range may be different depending on the case of applicationand the motor design, and is to be selected individually. With thetwo-pole motor represented by way of FIG. 2, this angular range is 90°after the zero-crossing of the U_(EMF) voltage. The curves A and B shownin FIG. 2 a represent the polarity of the voltage U_(EMFA) and U_(EMFB)induced in the windings of two poles. Since it is the case of a two-polemotor and the windings of the poles are offset by 90° to one another,the angular range of 90° may be determined solely by evaluating thezero-crossings of the induced voltages in both windings, as FIG. 2 amakes clear, without having to measure the angle itself. Since thewindings are arranged offset to one another by 90°, on account of thegeometrical relationships it results that when the induced voltage inthe lagging winding B has a zero-crossing, the prior zero-crossing ofthe induced voltage must lie back by 90°. Thus the angular range inwhich the firing is to be effected according to rule c may be determinedsolely by detecting the successive zero-crossings of the inducedvoltages U_(EMFA) and U_(EMFB). FIG. 2 a l which represents the startingof the motor in a manner which is analogous to FIG. 1, illustrates thatthe estimation of the angular range which is taken on account of thisgeometric relationship is quite accurate. When the motor has departedfrom the low starting rotational speeds and is operated at a constantrotation speed, the desired angular range may alternatively also bedetermined by time measurement from the preceding period, which resultsfrom the right part of FIG. 2 a. The time intervals resulting from FIG.2 a, in which a firing, i.e. a switching of the triac connecting thewinding A to the supply voltage U_(V) are effected, are indicated inFIG. 2 b at 1. The triac for winding A may therefore be switched wherethe curve according to FIG. 2 b assumes the value 1, should it be thecase that firing rule c is to be observed.

FIG. 3 illustrates how the firing rule d is to be implemented. As in thepreviously described diagrams, time is also represented on thehorizontal axis in the diagrams of FIGS. 3 a, b and c. In FIG. 3 a, thepolarity of the supply voltage (positive at 1, negative at 0) is shownon the vertical [axis], in FIG. 3 b the polarity of the voltage U_(EMF)induced in the winding to be connected and in FIG. 3 c the timeintervals which result according to rule d in order to fire the triac ofthe associated winding, i.e. to connect this winding to the mainssupply.

Rules d states that the triac is only to be fired when the zero-crossingof the supply voltage U_(V) lies in front of the expected zero-crossingof the voltage U_(EMF) induced in the winding to be connected, assumingthe same direction, i.e. that the polarity change of the zero-crossingof the supply voltage and of the induced voltage which are to beconsidered are in the same direction, i.e. in both cases should run fromplus to minus or also from minus to plus. Since firing rule d withrespect to the zero-crossing of the supply voltage presupposes a futureevent which with regard to measurement technology may yet not bedetermined, this event must be calculated by way of precedingzero-crossings of the induced voltage, or be estimated or evaluated inanother suitable manner. For this, it is useful to detect the precedingzero-crossings and on account of their distances or their distancechange, to determine an expected zero-crossing, by way of which rule dmay then be observed. FIG. 3 c, where the curve assumes the value 1,indicates the time intervals in which a firing of the triac of theassociated winding is to be effected according to rule d. As thetemporal region 0.54 to 0.6 as well as 0.64 to 0.68 of the curveaccording to FIG. 3 c illustrates, here no switching intervals result,since in these regions either the zero-crossing of the supply voltageU_(V) does not lie in front of the expected zero-crossing of the voltageUEMF induced in the winding to be connected, or the direction isreversed. This limitation of the switching serves the purpose ofpreventing a current flow producing a negative moment.

According to rule e the firing is to be effected in a manner such thatthe angle between the voltage U_(EMF) induced in the winding to beconnected and the supply voltage U_(V) assumes a predefined value. Thisrule represents a type of optimisation method and is represented by wayof FIG. 4.

The temporal course of the polarity of the supply voltage is representedin FIG. 4 a, wherein 1 represents a positive polarity and 0 a negativeone. FIG. 4 b represents the temporal course of the polarity of thevoltage U_(EMF) induced in the winding to be connected. FIG. 4 c showsthe temporal course of the polarity of the voltage across the switch(triac), i.e. the polarity of the voltage resulting from the supplyvoltage U_(V) and the voltage U_(EMF) induced in the winding to beconnected. FIG. 4 d shows the optimisation of the point in time of thefiring which is effected according to rule e, and FIG. e the currentcourse in the winding. According to this, the angle β between thezero-crossing of the supply voltage U_(V) and the zero-crossing of theinduced voltage U_(EMF) in the winding to be connected should beconstant, i.e. should correspond to a predefined value. In order toachieve this, the firing angle α calculated from the zero-crossing ofthe supply voltage is to be accordingly set until this angle β=constantis the case. The angle β is thus controlled with a closed loop by way ofadjusting the firing angle α. The signal according to FIG. 4 c is notrequired for these optimisation controls.

An alternative optimisation of the firing may be effected according torule f, as is represented by way of FIG. 5 a to e. Accordingly, thefiring is to be effected such that the angle T₂ between the point intime when the current I_(W) (see FIG. 5 e) in the winding to beconnected assumes the value 0 (results from FIG. 5 c) up to the point intime in which the induced voltage U_(EMF) in this winding assumes thevalue 0 corresponds to the angle T₁, which lies between the previouszero-crossing of the induced voltage and the current point in time offiring. The courses of the curves according to FIG. 5 illustrate this indetail, the representations according to a to c correspond to those ofFIG. 4 a to c, and these are referred to inasmuch as this is concerned.In this case T₂ is firstly to be determined and then the firing angle αis to be varied such that T₁=T₂, thus these angles are equally large.Alternatively one may also place a predefined relationship on theseangles. These firing rules in particular serve for a smooth running ofthe motor and a uniform load distribution.

FIG. 6 represents an equivalent circuit diagram of a two-pole motor byway of example. The motor comprises two poles which are offset by 90° toone another, and corresponding windings A and B, wherein each of thewindings A and B is connected to the supply voltage U_(V) by way of atriac T2 and triac T3 respectively. The triacs T2 and T3 are switchedaccording to the previously described firing rules, so that the windingA and the winding B are subjected to the supply voltage U_(V), andspecifically for so long until the current in this winding becomes zero.With the motor represented by way of FIG. 6, via a third triac T4 onemay yet additionally connect a capacitor C which effects a phase shiftof the windings A and B to one another. This capacitor is connected whenrunning at a constant and synchronous rotational speed and effects asmooth, uniform and thus quiet running of the motor. One must makespecial provisions when connecting and disconnecting the capacitor. Onconnecting the capacitor it is to be ensured that the triac T3 is notconnected through before the triac T4 is switched, whilst taking atleast the firing rules a and b into account.

The connection of the capacitor C is thus effected when the currentflowing through the triac T3 is zero since T3 is then opened. This maybe detected in that either the voltage across T3 is measured or onewaits for a temporal interval, for example of half a period of thesupply voltage U_(V) until T4 is switched.

With the motor represented by way of FIG. 6, the winding A is divided upinto two part windings A1 and A2, wherein the part winding A2 may beactivated by way of triac T1, whereas the whole winding consisting ofthe part windings A1 and A2 connected in series are switched by way oftriac T2. The division of the winding A into part windings A1 and A2,when comparatively high operating angles result, in particular at asynchronous speed, permits a part of the winding, specifically forexample the winding part A1, to be disconnected in order in this mannerto achieve smaller operating angles and thus a smoother running of themotor. This measure is particularly suitable for accommodatingfluctuations in the mains and inasmuch as this is concerned is not soimportant if a stable mains supply is ensured in another manner. In thesame manner one omit the connectable capacitor C, in particular if anoptimisation of the efficiency is not necessary. This also applies toswitch T3 which permits a separate switching of the winding B. If aphase-angle control is not necessary for B, then this triac T3 may beomitted, but then however a supersynchronous operation of the motor isno longer possible. The switch T3 may therefore be omitted when themotor is designed only for synchronous or subsynchronous operation.

Common to all arrangements is a rotational speed control circuit R1which activates the switches T1 to T4 and controls [with a closed-loop]the rotational speed according to the rules a to d by way of activatingthe switches T1 to T4 in dependence on the nominal value setting n_(nom)and the electrical variable E which results from the supply voltageU_(V) and the induced voltages U_(EMF) of the individual windings orwinding parts. It is indeed only possible to control a synchronous motorat practically any rotational speed by way of this control circuit R1which applies the firing rules a to d.

A further control circuit R2 is provided in order to implement theefficiency optimisation rules e and f, which activates the switches T1to T4 according to rules e and f as well as the rules a to d of thecontrol circuit R1.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications within the spirit and scope of thepresent invention as defined by the appended claims.

1. A single-phase synchronous motor which is supplied with alternating current and which is controlled in accordance with a method for controlling the firing angle of a single-phase electric motor supplied with alternating current, by way of at least one locking electronic switch between the supply voltage and at least one motor winding, with which the switch or switches are switched according to one or more of the following conditions: a) the voltage (EMF) induced in the winding to be connected has the same polarity as the supply voltage, b) the voltage (EMF) induced in the winding to be connected, with the same polarity, is smaller than the supply voltage with regard to magnitude, c) the voltage (EMF) induced in the winding to be connected, with respect to its zero-crossing is located in a predefined angular range, assuming the same polarity of the induced voltage and the supply voltage, d) the zero-crossing of the supply voltage lies in front of the expected zero-crossing of the voltage (EMF) induced in the winding to be connected, assuming the same direction, e) the firing is effected in a manner such that the angle between the voltage (EMF) induced in the winding to be connected and the supply voltage assumes a predefined value, f) the firing is effected in a manner such that the angle between the point in time when the current in the winding to be connected assumes the value zero up to the point in time at which the induced voltage (EMF) in this winding assumes the value zero is dependent on the angle which lies between the previous zero-crossing of the induced voltage and the current point in time of firing, wherein the motor comprises a permanent magnet rotor with at least one winding (A, B) which is arranged in the stator and which may be subjected to the supply voltage (U_(v)) by way of a locking electronic switch (T2, T3), and with an electronic control circuit (R1) (speed control circuit) which controls a settable nominal rotational speed (n_(nom)) whilst applying the firing rules according to claim elements a) to d), and wherein a further control circuit (R2) is provided for optimising the efficiency, which controls whilst applying the optimization rules according to claim elements e and f.
 2. A single-phase synchronous motor which is supplied with alternating current and which is controlled in accordance with a method for controlling the firing angle of a single-phase electric motor supplied with alternating current, by way of at least one locking electronic switch between the supply voltage and at least one motor winding, with which the switch or switches are switched according to one or more of the following conditions: a) the voltage (EMF) induced in the winding to be connected has the same polarity as the supply voltage, b) the voltage (EMF) induced in the winding to be connected, with the same polarity, is smaller than the supply voltage with regard to magnitude, c) the voltage (EMF) induced in the winding to be connected, with respect to its zero-crossing is located in a predefined angular range, assuming the same polarity of the induced voltage and the supply voltage, d) the zero-crossing of the supply voltage lies in front of the expected zero-crossing of the voltage (EMF) induced in the winding to be connected, assuming the same direction, e) the firing is effected in a manner such that the angle between the voltage (EMF) induced in the winding to be connected and the supply voltage assumes a predefined value, f) the firing is effected in a manner such that the angle between the point in time when the current in the winding to be connected assumes the value zero up to the point in time at which the induced voltage (EMF) in this winding assumes the value zero is dependent on the angle which lies between the previous zero-crossing of the induced voltage and the current point in time of firing, wherein the motor comprises a permanent magnet rotor with at least one winding (A, B) which is arranged in the stator and which may be subjected to the supply voltage (U_(v)) by way of a locking electronic switch (T2, T3), an electronic control circuit (R1) (speed control circuit) which controls a settable nominal rotational speed (n_(nom)) whilst applying the firing rules according to claim elements a to d, a phase-shifting component connected in series to the at least one motor winding, and at least one further locking electronic switch (T4), to which the phase-shifting component (C) may be connected, and wherein the phase-shifting component is a capacitor (C) and the electronic switches (T1–T4) are triacs.
 3. A method for controlling the firing angle of a single-phase electric motor supplied with alternating current, by way of at least one locking electronic switch between the supply voltage and at least one motor winding, with which the switch or switches are switched according to one or more of the following conditions: a) the voltage (EMF) induced in the winding to be connected has the same polarity as the supply voltage, b) the voltage (EMF) induced in the winding to be connected, with the same polarity, is smaller than the supply voltage with regard to magnitude, c) the voltage (EMF) induced in the winding to be connected, with respect to its zero-crossing is located in a predefined angular range, assuming the same polarity of the induced voltage and the supply voltage, d) the zero-crossing of the supply voltage lies in front of the expected zero-crossing of the voltage (EMF) induced in the winding to be connected, assuming the same direction, e) the firing is effected in a manner such that the angle between the voltage (EMF) induced in the winding to be connected and the supply voltage assumes a predefined value, f) the firing is effected in a manner such that the angle between the point in time when the current in the winding to be connected assumes the value zero up to the point in time at which the induced voltage (EMF) in this winding assumes the value zero is dependent on the angle which lies between the previous zero-crossing of the induced voltage and the current point in time of firing, wherein the zero-crossings and polarity of the voltage induced in a winding is measured with the supply voltage switched off.
 4. A method for controlling the firing angle of a single-phase electric motor supplied with alternating current, by way of at least one locking electronic switch between the supply voltage and at least one motor winding, with which the switch or switches are switched according to one or more of the following conditions: a) the voltage (EMF) induced in the winding to be connected has the same polarity as the supply voltage, b) the voltage (EMF) induced in the winding to be connected, with the same polarity, is smaller than the supply voltage with regard to magnitude, c) the voltage (EMF) induced in the winding to be connected, with respect to its zero-crossing is located in a predefined angular range, assuming the same polarity of the induced voltage and the supply voltage, d) the zero-crossing of the supply voltage lies in front of the expected zero-crossing of the voltage (EMF) induced in the winding to be connected, assuming the same direction, e) the firing is effected in a maimer such that the angle between the voltage (EMF) induced in the winding to be connected and the supply voltage assumes a predefined value, f) the firing is effected in a manner such that the angle between the point in time when the current in the winding to be connected assumes the value zero up to the point in time at which the induced voltage (EMF) in this winding assumes the value zero is dependent on the angle which lies between the previous zero-crossing of the induced voltage and the current point in time of firing, wherein it is determined whether the voltage induced in the winding to be connected is smaller than the supply voltage with regard to magnitude given the same polarity, in that the voltage across the switch of this winding is measured and is evaluated depending on polarity. 